1. Field of the Invention
The present invention relates a method of determining a synchronous signal pattern in a format of information to be recorded on a medium in an information recording apparatus such as, e.g., an optical disk memory or the like and a method of and device for recording the synchronous signal pattern determined by the former method on the medium.
2. Related Background Art
FIG. 1 shows one example of an ISO-standardized sector format of a WORM type or rewritable type optical disk of a 5.25 in. continuous servo tracking system. Table 1 shows patterns and meanings of the symbols with which the respective portions of FIG. 1 are marked.
TABLE 1 ______________________________________ Symbols Meanings Patterns ______________________________________ SM Sector mark 5-byte length. Pattern is "1.sup.10 0.sup.6 1.sup.6 0.sup.14 1.sup.6 0.sup.6 1.sup.6 0.sup.6 1.sup.10 0.sup.2 1.sup.1 0.sup.2 1.sup.1 0.sup.2 1.sup.1 0.sup.1 " (1.sup.a,0.sup.b are code bits and indicate that "1" continues by the number a, while "0" continues by the number b. This corresponds to code bits of Y sequence in modulation. VF0123 Continuous data VF01-010010010010 . . . 0010 (12 pattern for bytes) PLL lock VF02-100100100100 . . . 0010 (8 bytes) 000100100100 . . . 0010 (8 bytes) VF03-VF01 VF02 indicates that any one of two patterns is selected by preceding CRC data pattern. AM Address mark Pattern has 16 code bits and is "0100100000000100". SYNC Synchronous 3-byte length. Pattern is signal of data "0100 0010 0100 0010 0010 portion 0010 0100 0100 1000 0010 0100 1000". ID Address 2 bytes are recorded as a track number by (2, 7) modulation, and 1 byte is recorded as a sector number by (2, 7) modulation. CRC ID portion error 2-byte CRC is recorded by detection code (2, 7) modulation, and generating polynomial is G(x) = x.sup.16 - x.sup.12 - x.sup.5 - 1
Postamble ID and CRC are recorded by variable-length words as in (2, 7) modulation. PA is therefore used when not settled by 2 bytes of CRC after modulation. ODF Offset detect- Consisting of specular (Offset ion mark in surface with no groove Detection tracking error and no preformat data Flag) detection using push-pull method Gap Gap No data in interval of 3-byte length FLAG Flag indicating Pattern to be set that writing continues "100" for has been 5 bytes executed ALPC Test portion 2-byte length is blank Auto Las- for controll- er Power ing power level Control) of laser DATA Area for writ- Consisting of 1024-byte user ing user data data, 233-byte CRC, ECC and Resync and 12-byte control information BUFFER Disk rotation- No written data al fluctuat- ion margin area RESYNC Intra DATA 16 code bits area sync 0010 0000 0010 0100 special code ______________________________________
Referring to Table 1, the VFO pattern is a signal pattern for synchronizing a voltage frequency oscillator (VFO) in a phase locked loop (PLL) circuit of an information recording/reproducing device. Further, in the example given above, the synchronous signal (SYNC) pattern of a data portion has a 3-byte length and is expressed by 48 code bits such as "0100 0010 0100 0010 0010 0010 0100 0100 1000 0010 0100 1000".
This ISO standard synchronous signal pattern is configured to have the following two major characteristics.
(1): The pattern has a sharp auto-correlation. PA0 (2): The pattern can be generated by (2, 7) modulation, and the modulation is completed by 3 bytes without excess and deficiency. PA0 (1): A true importance of the synchronous signal pattern of the recording and/or reproducing device lies in not an auto-correlation function but a sharpness of the correlation property between the recording pattern including the VFO pattern and the matching filter. It is therefore possible to surely obtain a more optimal synchronous signal pattern than in the prior art. PA0 (2): When looking at the sharpness of the correlation property, there is no necessity for considering the sharpness behind (right side) the correct position. The time required for obtaining the optimum synchronous signal pattern is thereby reduced. PA0 "100100010001001010101010000100101001", PA0 "100101001010010100010101010010001001", PA0 "100101001010010101010100010010001001" and PA0 "010101010100100010010100101001001001". PA0 "010010100101001010101010001001000100" and "010010100101001010101000100010010001".
If the condition (1) is not satisfied, there increases a probability to cause a wrong synchronization due to a bit error. When the wrong synchronization takes place, the sector thereof cannot absolutely be reproduced.
Whereas if the condition (2) is satisfied, the generation of the synchronous signal pattern is facilitated during the recording process, and a small-scale circuit may suffice. Further, in the example given above, the (2, 7) modulation is used in the data portion. Hence, the record of the synchronous signal by the same (2, 7) modulation implies that no special consideration is paid to a recording/reproducing signal property on the medium and a property of the detection system.
In contrast with this, we have found out that the correlation property with the VFO pattern has a major role when determining a superiority and inferiority of the synchronous signal pattern from a sharpness of the auto-correlation property. In other words, the conventional method of determining the superiority and inferiority of the pattern from the sharpness of the auto-correlation property does not give any consideration to the correlation property with the VFO pattern. Namely, in the prior art, the optimum pattern is determined by considering the sole synchronous signal pattern.
Therefore, in accordance with the conventional determining method, if no signal exists in front and in rear of a certain synchronous signal pattern, an output of a matching filter exhibits the sharpest peak in some cases. Based on the conventional method, such a synchronous signal pattern is to be optimal. Supposing that a given VFO pattern is disposed in front of the thus determined synchronous signal pattern, however, the output of the matching filter does not necessarily indicate that the synchronous signal pattern has the sharpest peak among all the patterns depending on a combination of the VFO pattern and the synchronous signal pattern in some cases. The above-described ISO pattern is an example thereof.
Besides, we point out the following defects inherent in the prior art.
That is, in the case of considering a conventional ordinary synchronous signal pattern detector, it has a predetermined threshold level with respect to the output value of the matching filter. The synchronous signal pattern is detected at the first timing when the output value exceeds the threshold level. This is a typical method.
FIG. 2 shows an example of a typical synchronous signal pattern detector. Referring to FIG. 2, signals read from a recording medium are sequentially inputted to a shift register 13. On the other hand, a predetermined correct synchronous pattern is stored in a memory 14. The signal inputted to the shift register 13 is compared bitwise or blockwise with the synchronous pattern stored in the memory 14. Outputted then from a coincidence number adding circuit 15 is a correlation value of the thus compared two patterns, i.e., the bit number in which the values coincide with each other. This correlation value is compared with a predetermined threshold value in a threshold comparison circuit 16. A pulse signal indicating that the synchronous pattern has been detected is outputted from a pulse output circuit 17 at a timing when the correlation value exceeds the threshold value. Upon outputting this pulse signal, a reproducing means reproduces the data recorded on the medium subsequently to the detected synchronous pattern.
Herein, if a plurality of synchronous signal pattern detection pulses are mistakenly outputted within one sector, the data number becomes incorrect, resulting in trouble in terms of the system. Hence, the pulse is generally outputted only in the first one detected position within the sector.
According to this method, after the synchronous signal pattern has been once detected, there is no influence, whether the sharp portion of the correlation exists afterward or not. Namely, the correlation property may not be considered after the correct position.